Renal dysfunction or failure and, in particular, end-stage renal disease, causes the body to lose the ability to remove water and minerals and excrete harmful metabolites, maintain acid-base balance, and control electrolyte and mineral concentrations within physiological ranges. Toxic uremic waste metabolites including urea, creatinine, uric acid, and phosphorus accumulate in the body's tissues, which can result in a person's death if the filtration function of the kidney is not replaced.
Dialysis is commonly used to replace kidney function by removing these waste toxins and excess water. In one type of dialysis treatment-hemodialysis-toxins are filtered from a patient's blood externally in a hemodialysis machine Blood passes from the patient through a dialyzer separated by a semi-permeable membrane from an externally-supplied dialysate. Water and toxins dialyze out of the blood through the semi-permeable membrane into the dialysate, which is then discarded. Hemodialysis treatment typically lasts several hours and must be performed under medical supervision three or four times a week, requirements that significantly decrease a patient's autonomy and quality of life. Also, since hemodialysis is performed periodically instead of continuously, the patient's condition and general well-being tend to be poor both immediately before hemodialysis (when toxin levels are high) and after hemodialysis (when electrolytes are imbalanced), resulting in the patient having symptoms that range from nausea and vomiting to edema.
Peritoneal dialysis is another type of dialysis treatment used to replace kidney function in which sterile, pyrogen-free dialysis solution (dialysate) is infused into the patient's peritoneal cavity. The peritoneal membrane serves as a natural dialyzer and toxic uremic waste metabolites and various ions diffuse from the patient's bloodstream across the membrane into the dialysis solution due to their concentration gradients. At the same time, water is drawn into the peritoneal cavity by an osmotic gradient. The dialysis solution is removed, discarded and replaced with fresh dialysis solution on a semi-continuous or continuous basis. Draining, discarding and replacing the large volumes of solution needed for peritoneal dialysis is still inconvenient, unwieldy and expensive, especially for peritoneal dialysis treatment at home instead of at a treatment center.
To address this problem, devices have been designed that reconstitute used dialysate from hemodialysis and/or peritoneal dialysis solution as opposed to discarding it. The dialysate can be regenerated in a machine employing a device that eliminates urea from the solution. For example, the original REDY® (REcirculating DYalysis) Sorbent System (Blumenkrantz et al., Artif. Organs 3(3):230-236, 1978) consists of a sorbent cartridge having five layers through which dialysate containing uremic waste metabolites flows in order to be regenerated. The spent dialysate flows through a purification layer that removes heavy metals (e.g., copper and lead) and oxidants (e.g., chlorine and chloramine), an aluminum oxide layer containing urease bound to some of the aluminum oxide which degrades the urea in the dialysate into ammonia and carbon dioxide gas, in equilibrium with ammonium carbonate, a zirconium phosphate layer that adsorbs the ammonium ions produced from urea degradation along with other cations (e.g., sodium, potassium, magnesium and calcium), a hydrated zirconium oxide layer that binds phosphate and other anions (e.g., fluoride and sulfate) in exchange for acetate, and an activated carbon layer that adsorbs other organic compounds (e.g., creatinine and uric acid).
Typically, the ion exchange resins used in devices such as the REDY® Sorbent System adsorb not only the urea degradation products, but also essential ions such as, for example, calcium and magnesium that have diffused into the dialysate. These ions must then be rapidly replaced in the patient; however, there currently exists no easy or convenient mechanism to do so. By comparison, current sorbent-based hemodialysis machines replace these essential ions continuously using a precision pump and associated valve and control mechanisms, devices that increase the weight and complexity of a hemodialysis machine, and would present similar problems for a peritoneal dialysis system.
There is, therefore, a need for a dialysate regeneration system that is more convenient, safe and effective and that significantly improves a patient's quality of life over current devices and methods.